1. Field of the Invention
The present invention relates to a starter for cranking an internal combustion engine, the starter having a one-way clutch.
2. Description of Related Art
An example of a starter having a one-way clutch is disclosed in JP-U-6-23742. A relevant portion of this starter is shown in FIG. 5 attached hereto. The one-way clutch 140 of this starter has a clutch-inner 130 that is coupled to an output shaft 150 by means of a helical spline. The clutch-inner 120 is rotatably supported by a ball bearing 100 which is held in a frame 110. A front portion 120 of the clutch-inner 130 is inserted into an inner ring of the ball bearing 100. The output shaft 150 having a pinion at its front end is pushed forward toward a ring gear of an engine so that the pinion engages with the ring gear. A rotational torque of an electric motor contained in the starter is transmitted to the output shaft 150 via the one-way clutch 140. In a starter disclosed in JP-U-58-96059, a ball bearing is arranged so that balls of the ball bearing directly contact a rotating shaft, thereby eliminating an inner ring of the bearing.
In the starter disclosed in JP-U-6-23742, the outer diameter of the clutch-inner 130 that carries the ball bearing 100 thereon cannot be freely designed because the outer diameter has to fit the inner diameter of the inner ring of the ball bearing 100. If the outer diameter of the clutch-inner 130 is enlarged to increase its mechanical strength, a larger ball bearing 100 has to be used. This makes the size of the starter large. It may be possible to use a specially designed ball bearing to suppress the size of the starter. This makes the starter expensive.
In the starter disclosed in JP-U-58-96059, the balls of the ball bearing directly contact a cylindrical outer circumference of the rotating shaft. Accordingly, it is impossible to retain lubricant on the shaft. If there is some lubricant adhering to the rotating shaft, the lubricant would be positioned apart from the balls when the rotating shaft shifts forward. Therefore, when the rotating shaft is driven by the engine via the pinion at a high speed, it is highly possible that seizing (or burn-in) occurs between the bearing balls and the rotating shaft. This is highly detrimental to durability of the starter. Further, foreign particles or dusts on the rotating shaft will be rolled in to the balls, thereby causing high abrasion.